Non deterministic virtual warning

[blueluna]

Adding a warning message when there is a non-deterministic selection of a virtual core during setup.

[olofk]

@a-will @HU90m Will this solve the non-determinism for virtual cores in OpenTitan? (cc @Razer6)

[olofk]

@blueluna Lint check fails. Make sure to run pre-commit install in the repo root so you get lint checks on every commit

[a-will]

@a-will @HU90m Will this solve the non-determinism for virtual cores in OpenTitan? (cc @Razer6)

It's a useful warning, at least! So build issues can be more readily explained in case someone forgot to add the implementing core to a core file.

If the user did specify which virtual core should be used, then #668 ensures that it actually would get used.

The last interesting bit might be not requiring the VLNVs to be placed in a core file (i.e. a mechanism to choose the cores from a command line option, adding to "requirements" alongside the tree generated by the system core). I just had to update about 200 core files to add implementing core specs for lint targets in OpenTitan, where the feature might have reduced that down to a single flow config file. 😅